Piezoelectric ultrasonic transducer



Aug. 2, 1960 R. D. MGGUNIGLE 2,947,336

PIEZOELECTRIC ULTRASONIC TRANSDUCER F i1ed April 29, 1958 INVENTOR.RICHARD D. MCGUNIGLE JMM ATTORNEY 2 Sheets-Sheet 1 United States Patent)6 PIEZOELECTRIC ULTRASONIC TRANSDUCER Richard D. McGunigle, NewBrunswick, N.J., assignor to Gulton Industries, .Inc., Metuchen, N.J., acorporation of New Jersey Filed Apr. 29, 1958, Ser. No. 731,744

8 Claims. (Cl. 310-83) Patented Aug. 2, 1 960 ice it to section 13 bymeans of threaded element 22 which is formed from the same piece ofstock as section 15. Threaded element 22 is threaded into threadedopening 17 which is carried by section 13. Tool end 16 is suitablyattached to the small end of section 15, by means of matching threads ontool end 16 and in the small end of section or by a set screw or similarmeans (attaching means not shown). In the form of my invention shown inthe figures, I prefer to fashion section 15 from stainless steel butother similar materials may also be used. Sections 11, 12 and 13 may, ifdesired, he formed from a unitary piece of stock. The acousticalcontinuity, when section is threaded into the balance of-mechanicaltransformer 10 and is so machined as to bottom mechanically in hole 17,is preserved by filling any gaps, especially at the shoulder, with epoxyresin. The epoxy resin generally comprises a base resin combined with aIt is a further object of my invention to provide such a mechanicaltransformer which is conical in shape and is provided with a pluralityof tapered sections whereby the cross section varies approximatelyexponentially.

It is a still further object of my invention to-provide 1;.

such a mechanical transformer which may be driven by a plurality ofelectromechanically sensitive bodies;

Other objects, features and advantages of my invention will be apparentduring the course of the following description when taken in conjunctionwith'the accorng panying drawings wherein:

Figure 1 is an elevational view of a preferred embodiment of myinvention,

Figure 2 is a top plan view of the embodiment of Figure 1,

Figure 3 is a cross-sectional view along the line 3-3 of Figure 1,viewed in the direction of the arrows, I

Figure 4 is a view similar to Figure 1 showing the upper portion of themechanical transformer in cross;- section and the lower portion inelevation,

1, shown).

Figure 5 is an elevational view, partly in cross-section,

showing the method of placing the electromechanically sensitive bodiesunder compression, and I Figure 6 is a cross-sectional view along theline 6-6 of Figure 1.

In the drawings, wherein, for the purpose of illustration, is shown apreferred embodiment of my invention,- the numeral 10 designates themechanical transformer, generally. Mechanical transformer 10 iscomprised of three sections, denominated 11, 13 and 15, and mountingflange 14. The larger base of mechanical transformer 10 is designated12. In its preferred form, I choose to fashion sections 11 and 13 andmounting flange 14 from a single piece of stock such as aluminum or likematerial. However, these elements may also be made in separate piecesand suitably bonded together.- Flange 14 is located at a velocity nodeso that the assembly may be supported properly without coupling off anyenergy or lowering the Q of mechanical transformer 10. At the velocitynodes, the slope of the lines which generate the surfaces of the taperedsections changes The slope of the line which generates the surface ofsection 11 has the smallest value, that of the line which generates thesurface of section 13 has a slightly larger value, and that of the linewhich generates the surface ofsection 15 has a slightly larger value.The slopes are so chosen that, taken together, the surface of mechanicaltransformer 10 approximates that of a surface of revolution whichhas-been generated by an exponential curve.

hardener such as, for example, metaphenylene diamine, and inert mineralfillers. Consistency can be controlled by the addition of diluents in amanner well-known in the art such as has been described in the articleentitled Where and How to Use Epoxies by Jerome Formo and Luther Bolstadon pages 99 and 104 of. Modern Plastics,

July 1955, volume 32, No. 11.

Electromechanically sensitive bodies 18 are preferably formed ofpiezoelectric ceramic consisting largely of barium titanate but otherpiezoelectric ceramics, ferroelectric ceramics or electromechanicallysensitive materials may be used with equally eflicacious results. Suchother materials include, among others, the natural piezoelectrics andthe magnetostrictives. Bodies 18 are solid cylinders, in the embodimentillustrated, and have applied to their end surfaces, by painting,evaporating, sputtering, or any other method well-known in the art,metallic electrodes 27 and 28 of silver or similar material. Electricalleads 30 are suitably attached by soldering or otherwise to electrode 28and electrical leads 31 are suitably attached through shim 27a toelectrode 27. Leads 30 are connected to ground lugs 30a and leads 31 areconnected to the high side of the ultrasonic generator (not Shims 27aare preferably formed from brass foil sheets about 5 mils thickwhich-are pressed into intimate contact against electrodes 27 by meansof 0- rings 26. Shims 27a are pretinned so that leads 31 can be solderedthereto. Leads 31 are carried away from y the assembly through holes 33in plate 19.

Hole 34 is provided in plate 19 to receive an adapter from an air supply(not shown) in order to admit cooling air into the space between thefour bodies 18. These spaces are made large enough to provide forelimination of the exhaust air around each body 18.

Bodies 18 are aflixed to mechanical transformer 10 by means of an epoxyresin 29, such as has been described above. The epoxy is baked for fourhours at F. which temperature is below the transformation 7 temperatureof bodies 18. The time and temperature I choose to fashion section 15from steel and to attach are interdependent and the time may beshortened if the temperature may be raised depending on the ceramictransformation temperature. temperature must be loweerd, the time mustbe increased. The epoxy may also be cured at room temperature, ifdesired, in which case the time must be increased considerably.

Plate 19 is rigid and is formed of a plastic molded on layers of linencloth for strength but may also be formed of other rigid plastics orconductive metals such as steel, brass and similar materials. Plate 19has cut therein grooves 25 which are of approximately the same radialdimensions as the various bases of the several el-ectromechanically'sensitive bodies 18 and of approximately ,5 the area of the surface ofthe base of each On the other hand, -if the v on bolts 21.

body 18. O-rings 26 which fit in grooves 25, are of the same shape asthe grooves and are formed of neoprene rubber or similar resilientmaterial. Holes are provided in. plate19 to receive bolts 21 which are,threaded at the ends as at 23 so as to mate with threaded holes; 24which are carried in base 12 of mechanical transformer 10. Insulator 2%)is formed of Teflon or similar material and is employed to insulateplate19 from ,bolts'21 and mechanical transformer 16.

Mounting flange 14 is provided with holes 32 into which mounting boltsor similar elements (not shown) may be inserted in order to support thecompleted assembly. p

The units of my invention are assembled in the following manner: 7 1 IBodies 18 are coupled to base 12 by means of a somewhat rigid type ofepoxy resin such as has been described heretofore. Then the bodies 18are clamped against base 12 to attain good mechanical strength in theassembly. This is accomplished by means of plate 19 which carriesgrooves 25 into which O-rings 26 are fitted and holes through whichbolts 21 are fed. The bolts 21 are coated with the epoxy resinheretofore described at 23 and are threaded into holes 24. Then all fourbolts are torqued down evenly so as to equalize pressure on all fourbodies 18. After adjustment, the entire assembly is baked in order toharden the epoxy resin and maintain permanent adjustment of the unit;

Since the activity of mechanical transformer 10 depends to a largeextent on the clamping pressure on the bodies '10, the relative activityis measured during assembly of the unit by the usual resonancetechniques (voltage vs.

frequency, etc.). I have found that up to a certain value of torque onbolts 21, as for example, 7 /2 inchpounds on A1 inch studs, there islittle change in electrical activity. However, when the units are used,-thermal expansion and the high accelerations to which some of the partsare subjected cause some change in the pressure Since I desire toachieve the highest compressional bias consistent with usable activity,'I have found that it is best to adjust the torque to the highest limitat which initial activity is slightly reduced. Then,

after a few minutes of use under excitation from the ultrasonicgenerator (not shown), the pressure level shifts resulting in a maximumcompressional bias with minimum damping effect.

It should be noted that all surfaces to which epoxy resin is applied aresandblasted and intensively cleaned in order to guarantee that solidbonds will be maintained despite the high acceleration to which thecombination is subjected.

By way of illustration and not by way of limitation of the scope of myinvention, following is an example of a mechanical transformer driven byfour electromecham ically sensitive bodies:

Mechanical transformer 10 is a full wavelength long at 20 kc. The base12 is 4" in diameter. Each body '18 is 1 /2" in diameter and 4%" long.Bodies 18 are driven in length mode and have an unloaded resonantfrequency of 20 kc. The entire assembly, including the tool end 16 andthe electromechanically sensitive bodies, is 14%" long, resonates at 19kc. and is one and a half wavelengths at 19 kc. The diameter of base 12is nearly in half wave radial resonance at this frequency but the muchhigher Q in the length mode reduces degenerate cross coupling at thispoint. The combination has a displacement gain of about 50 and anelectrical input Q of 140. a

It is within the contemplation of my invention to i utilize a singleelectromechanically sensitive body in place of the four shown anddescribed or to use any other number of such bodies. It is also withinthe scope of my invention to operate ultrasonic devices such as I havedescribed at other frequencies than that set forth in 5' the exampleabove.

It is consistent with and within the contemplation of my invention touse a rigid plate which is larger in diameter than the large base of themechanical transformer and the holes for the clamping bolts are locatedso that the bolts clear the mechanical transducer base and are threadedinto or similarly aflixed to the mounting flange. This method ofclamping, since it is accomplished ata nodal surface, results in novibration in the bolts, insulators, and the rigid plate.

Furthermore, the number of tapered sections making up the mechanicaltransformer may be more or less than the three illustrated and shown. Asthe number of tapered sections is increased, the overall surfaceconfiguration approaches one generated by an exponential curve.

While I have described my invention by means of specific examples and ina specific embodiment, I do not wish to be limited thereto, for obviousmodifications will occur to those skilled in the art without departingfrom the spirit and scope of the invention.

Having thus described my invention, I claim:

7 1. An ultrasonic device comprising a tapered mechanical transformersubstantially conical in shape, a plurality of electromechanicallysensitive bodies affixed to the larger base of said mechanicaltransformer, a rigid plate carrying grooves therein, said mechanicaltransformer comprising first, second and third tapered sections, saidfirst tapered section being adjacent the base with the largest area,said second tapered section having its larger base adjacent the smallerbase of said first tapered section, said third tapered section havingits larger base adjacent the smaller base of said second taperedsection, the line generating the surface of said first tapered sectionhaving the smallest slope, the line generating the surface of saidsecond tapered section having a greater slope than having a greaterslope than that generating the surface of said second tapered section,the transitions from one said tapered section to the next adjacenttapered section being at a velocity node of said mechanical transformer,said rigid plate being at the ends of said electromechanically sensitivebodies opposite the ends affixed to said mechanical transformer, each ofsaid grooves being of approximately the same dimension as the perimeterof the surface of the electromechanically sensitive body to be clampedand whose area is less than approximately the area of said surface, aresilient member within said groove and in contact with saidelectromechanically sensitive body, acoustic transmission means incontact with each said electromechanically sensitive body and the largerbase of said mechanical transformer, means for applying compressionbetween said rigid plate and said mechanical transformer, and means forinsulating said rigid plate from said mechanical transformer.

2. An ultrasonic device as described in claim 1 including means forsupplying excitation to said electromechanically sensitive bodies.

3. An ultrasonic device as described in claim 1 wherein saidelectromechanically sensitive bodies are composed largely ofpiezoelectric ceramic.

4. An ultrasonic device as described in claim 1 wherein said means forapplying compression between said rigid plate and said mechanicaltransformer comprises a plurality of bolts running between said rigidplate and a mounting flange, said mounting flange being at thetransition from said first tapered section to said second taperedsection.

5. An ultrasonic device comprising a tapered mechanical transformersubstantially conical in shape, at least one electromechanicallysensitive body affixed to the larger base of said mechanicaltransformer, a rigid plate carrying grooves therein, said mechanicaltransformer comprising first, second and third tapered sections, saidfirst tapered section being adjacent the base with the largest area,said second tapered section having its larger base adjacent the smallerbase of said first tapered section, said third tapered section havingits larger base adjacent the smaller base of said second taperedsection, the line generating the surface of said first tapered sectionhaving the smallest slope, the line generating the surface of saidsecond tapered section having a greater slope than that generating theslope of said first tapered section, the line generating the surface ofsaid third tapered section having a greater slope than that generatingthe surface of said second tapered section, the transitions from onesaid tapered section to the next adjacent tapered section being at avelocity node of said mechanical transformer, said rigid plate being atthe end of said electromechanically sensitive body opposite the endaifixed to said mechanical transformer, said groove being ofapproximately the same dimension as the perimeter of the surface of saidelectromechanically sensitive body and whose area is less thanapproximately the area of said surface, a resilient member within saidgroove and in contact with said electromechanically sensitive body,acoustic transmission means in contact with said electromechanicallysensitive body and the larger base of said mechanical transformer, meansfor applying compression between said rigid plate and said mechanicaltransformer, and

means for insulating said rigid plate from said mechanical transformer.

6. An ultrasonic device as described in claim 5 wherein saidelectromechanically sensitive body is composed largely of piezoelectricceramic.

7. An ultrasonic device as described in claim 5 including means forsupplying excitation to said electromechanically sensitive body.

8. An ultrasonic device as described in claim 5 wherein said means forapplying compression between said rigid plate and said mechanicaltransformer comprises a plurality of bolts running between said rigidplate and a mounting flange, said mounting flange being at thetransition from said first tapered section to said second taperedsection.

References Cited in the file of this patent UNITED STATES PATENTS2,704,333 Calosi et al Mar. 15, 1955 2,818,686 Weiss Jan. 7, 19582,834,158 Peterrnann May 13, 1958 FOREIGN PATENTS 620,004 Great BritainMar. 17, 1949

